Down regulation or desensitization of endocrine cells has been demonstrated in a variety of endocrine tissues including the ovary. The process is generally characterized by loss of specific receptors and sometimes a sustained refractory period. Another process, luteolysis, which is unique to the ovary is also characterized by loss of receptors and impaired ability to secrete steroids. Although a good deal of information is available concerning the hormonal and receptor changes during down regulation and luteolysis, little is known about the receptor-receptor interactions during the two processes. The overall objectives of the proposed research are therefore to define down regulation (induced by LH) and luteolysis (induced by PGF2Alpha and possibly by LHRH agonists) in terms of the turnover rates of LH, Prolactin and lipoprotein receptors with respect to general membrane turnover. Specifically, the study will be divided into three parts: 1. Down regulation and luteolysis will be compared with respect to endocytic activities and overall membrane turnover in the corpus luteum. 2. Down regulation and luteolysis will be examined with respect to the metabolic fate of LH and Prolactin receptors in the corpus luteum. 3. The temporal relationship of the uptake and metabolism of lipoproteins and their receptors during down regulation and luteolysis will be studied. To accomplish these goals, we propose to use a combination of radiotracer, biochemical, cytochemical and ultrastructural approaches to study the interaction of all the functionally important ovarian receptors during these two processes. The completion of the proposed research will advance our knowledge in the actual mechanism ovarian functions are regulated and will contribute to our understanding toward the control of various pathological states and the aging process of the ovary.